Definition

The dietary cation-anion difference (DCAD) of a feed material or ration is determined by the balance between the positively charged ions (cations) and the negatively charged ions (anions). The DCAD is expressed in milli-Equivalents (mEq).

• The main cations are sodium (Na) and potassium (K), which have a basic effect in the body.
• The main anions are chloride (Cl) and sulphur (S), which have an acidic action in the body.

Calculation formula

You can calculate DCAD using the following formula:

DCAD (mEq/kg) = (Na (mg/kg)/23.0) + (K (mg/kg)/39.1) - (Cl (mg/kg)/35.5) - ((S (mg/kg) x 2)/32.1)

Role of DCAD in cow nutrition

DCAD is often used as a nutrient in the diet of dry cows. Just before calving, a cow’s calcium requirement rises sharply. When the calcium in the animal does not become available quickly enough, the risk of milk fever increases.

It is therefore advisable to provide dry cows with a ration with a negative DCAD. This can be achieved by:

• Providing special minerals that are relatively high in chloride and sulphur (although these are not very tasty).
• A ration with a low DCAD, the excretion of (acid) anions in the urine increases, while the pH of the blood and urine decreases:
  • Greater calcium resorption from the bones
  • More calcium excretion through the urine.

The calcium metabolism in the animal is thus activated and the risk of milk fever is reduced. After calving, the DCAD should be positive again for optimal feed intake and milk production.

Practical considerations

• Controlling these factors with roughage is not sufficient, as no significant difference in DCAD can be achieved this way.
• To properly apply DCAD nutrition, it is very important to know the exact minerals in the roughage, especially sodium, potassium, chlorine and sulphur.
• Without this knowledge, it is impossible to apply DCAD nutrition properly.

DCAD Values in common roughages (mEq/kg DM)

Eurofins Agro, data 2009–2013

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